Overlapped document detector

ABSTRACT

A document handling system is disclosed in which the documents are serially-fed along a predetermined path. The system further includes a sensor apparatus to detect any overlapped feeding of the documents.

United-States Patent Inventor Richard E. Milford Phoenix, Ariz. Appl.No. 765,062 Filed Oct. 4, 1968 Patented May 11, 1971 Assignee HoneywellInformation Systems Inc.

OVERLAPPED DOCUMENT DETECTOR 10 Claims, 4 Drawing Figs.

U.S. Cl .1 271/47, 27l/57,250/l19 Int. Cl B65h 7/12 Field ofSearch271/47,57; 209/1 17.7; 250/219 (1) (dc), 223

i o 11'' S 3! H D24 References Cited UNITED STATES PATENTS 3,023,9003/1962 Thier 209/1 11.7 3,034,643 5/1962 Keller et al. 209/1 11.73,356,853 12/1967 Rottman 209/1 11.7

Primary ExaminerEvon C. Blunk Assistant Examiner-Joseph WegbreitAttorneysGeorge K. Powers, Joseph B. Forman, Frank L. Neuhauser, OscarB. Waddell and Edward W. Hughes Patented May 11, 1971 3,578,315

2 Sheets-Sheet l O 10 O O O 0 1a 16 24 1; j 16 10 1e 5 l 55 um 19 14 v H[MU 1 w? I in; 17 10 13 16 2;

sum I INVENTOR. Ira l? Ha /4,80 c. Maven OVERLAPPED DOCUMENT DETECTORBACKGROUND OF THE INVENTION This invention relates generally to anapparatus for the detection of the condition of overlapped documents asthey are fed from a document supply to a work station along apredetermined path and more particularly to a system employing aphotosensitive device for detecting overlapped documents in serial-feddocument handling equipment.

1. FIELD OF THE INVENTION In high speed data processing systems,information processed by the system is normally supplied from anexternal source. One such external source in common usage today isso-called data handling equipment which furnishes information to thedata processing system from a variety of generally translucentinformation bearing media such as bank checks, deposit slips, bills,stubs, and specially designed forms.

Document handling equipment of this nature nonnally includes an inputhopper containing a supply of documents from which individual documentsare transported in serial fashion along a document path to a workstation. This work station will perform a function such as reading theinformation contained on the document after which the documents aretransported to other work stations or directly to an output hopperdepending on the particular document handling function required.

The serial feeding as hereinbefore described results in gaps between thesuccessively transported documents. These gaps are important in thatthey permit the document handling equipment to identify the work stationoutput as a series of individual records rather than a continuous streamof information. The gaps also allow sufficient time for any mechanicalfunctions to transpire such as deflection into the reject hopper.Occasionally documents are improperly fed in a partial or completeoverlapped condition resulting in errors. such as partial or completeloss of information on the overlapped documents.

2. DESCRIPTION OF THE PRIOR ART To prevent work station errors which mayresult from an overlapped condition of documents being transportedwithin document handling equipment, some means must be provided fordetecting this condition so that corrective measures may be taken. Inthe customary apparatus, the detection of an overlapped documentcondition is accomplished by a sensing apparatus which produces a signalupon detecting the presence of overlapped documents. This signal isemployed to inactivate the workstation during the passage of theoverlapped documents and directs them to a reject hopper. The rejecteddocuments may then be removed from the reject hopper for subsequentreprocessing.

In the prior art, several systems have been provided for detectingoverlapped documents in document handling equipment. One such systememploys a photosensitive device and a light source disposed on oppositesidesof a document path. Light rays emanating from the light source willcross the document path and impingeon the photosensitive device. Theintensity of the impinging light rays varies from full value with nodocument between the light source and the photosensitive device, to anattenuated value for a single document arranged between the light sourceand the photosensitive device, to a further attenuated value foroverlapped documents. The photosensitive device will sense the lightrays and produce signals representative of the amount of light impingingon its photosensitive surface. The signals produced by thephotosensitive device are coupled to an amplifier that is adjusted todeliver an overlapped document signal upon sensing the second attenuatedvalue.

This type of device is not satisfactory because the photosensitivedevice is subjected to large variations in the amount of impinging lightwhich relegates the differential between first and second attenuatedvalues to a relatively small portion of the photosensitive devicesoperating range. Thus, the difference between the light attenuated by asingle thin document and that attenuated by overlapped thin documents isoften insufficient to be satisfactorily detected by the photosensitivedevice.

Another prior art device utilizing the previously described principlesfurther includes an air supply for separating the overlapped documents.The separation of the overlapped documents results in an increase in thedifferential between the attenuated values of a single thin document andoverlapped thin documents to a point where the difference can bedetected. This prior art device is also not completely satisfactory dueto its inability to separate documents that are stapled, taped orotherwise stuck together.

Systems of the type just described generate signals representative ofthe conditions sensed as hereinbefore described. To insure properdetection of overlapped documents, the levels of these signals must notbe allowed to vary outside of predetermined limits. To compensate forsignal level variations which would result if a batch of documents beingprocessed differed from a preceding batch in such factors as documentthickness, paper density, etc., it is customary in the art to providefor manual adjustment of the gain of the signal amplifiers. Therefore, aneed exists for a self-adjusting system that will maintain the outputsignal levels within predetermined limits.

SUMMARY OF THE INVENTION To alleviate the problems of the prior art, thedocument sensing system of the present invention utilizes a photosensitive device positioned to respond to only that light which is diffusedby its passage through a document to produce a signal representative ofoverlapped documents. The signal thus produced may be coupled to anautomatic control circuit for delivery to other components within thedocument handling equipment.

It is, therefore, one object of this invention to provide an improvedsystem for detecting overlapped translucent items.

Another object is to provide-an improved system for detecting thinoverlapped documents.

A further object of this invention is to provide an improved system fordetecting overlapped documents when thedocuments are physically united.

A still further object is the provision of an overlapped documentdetector system which automatically adjusts for signal level variancesbetween successively processed batches of documents.

The foregoing and other objects of this invention, the various featuresthereof as well as the invention itself, may be more fully understoodfrom the following description when read together with the accompanyingdrawings, in which:

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic view showing adocument handling device incorporating the present invention;

FIG. 2 is an enlarged plan view of a portion of the document handlingdevice, partially in section, illustrating the features of theinvention;

FIG. 3 is a block diagram of the logic circuitry of the invention; and

FIG. 4 is a timing chart illustrating the relationship between thesignals occurring in the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT tioned to engage the topdocument in the input hopper and effect its movement into positionbetween the first of a series of feed belts l4 and a counter rotatingrestraining belt 15. The feed belts l4 advance the documents along thedocument path while the restraining belt reduces the possibility offeeding more than one document at a time. In some instances, however,more than one document will be fed along this path at one time, therebycreating an overlapped condition. The document path 12 is defined by thefeed belts 14 positioned on one side of the path of movement of thedocuments and on the opposite side of this path by a plurality ofrollers 16 spacedly arranged along a bedplate 17. The documents beingconveyed along the document path 12, in the direction indicated by arrow18, will pass an overlapped document sensor 19 and then advance througha work station 20 to an output hopper 21. When an overlapped documentcondition occurs, a signal will be generated by sensor 19 and a controlcircuit 39 which temporarily inactivates the work station 20 andenergizes a gate 22 which directs the overlapped documents into a rejecthopper 23. Sensor 19 responds to directly radiated light and diffusedlight in its operation. Directly radiated light is that light whichtravels in a straight line from a light source. and diffused light isthat light which is scattered by its passage through an object. Sensor19 employs well-known light sensitive elements such as siliconphotocells having photovoltaic properties. For purposes of thisembodiment, the photocells illustrated produce electrical signalsproportional to the amount of light impinging on their sensitivesurfaces. Such devices are illustrated and described in Millman, VacuumTube and Semiconductor Electronics," published by Mc- Graw-Hill,l958,pp. 152 through I54.

The overlapped document sensor 19, best seen in FIG. 2, is positionedadjacent to the document path 12 and is aligned with an aperture 24 inbedplate l7. Aperture 24 provides an opening for radiated light from alight source 25 to cross the document path 12 to impinge upon sensor 19.

Sensor 19 comprises a housing 26 which defines cavity 27 having a recess28 arranged within the cavity. Recess 28 is defined by a bottom surface29 and a sidewall 31. A photocell 30 is affixed to surface 29 and isshielded from directly radiated light by sidewall 31. Cavity 27 isdesigned so that directly radiated light is partially absorbed by lowreflection qualities of its walls. The direct reflection that does takeplace is directed away from the photocell 30. Diffuse reflection in thecavity is minimal and will not affect the operation of the photocell 30.The design of the cavity 27 and the positioning of the photocell 30within the recess 28 results in the photocell responding only to lightwhich is diffused by its passage through a single document or throughoverlapped documents. A second photocell 32 is mounted in housing 26upstream from cell 30 relative to document flow along path 12, and isresponsive to directly radiated light from source 25 through aperture24. A third photocell 33 is mounted within housing 26 downstream fromcells 30 and 32 and is also responsive to directly radiated light fromsource 25 through aperture 24. Housing 26 is further provided with atransparent window pane 34 closing cavity 27 which prevents dust andforeign material from collecting on the cells, thereby decreasing theirsensitivity.

Cells 32 and 33 are employed to detect the presence of a document inpath 12 between sensor 19 and light source 25. The absence of a documentin path 12 and across aperture 24 causes directly radiated light toimpinge on cells 32 and 33, causing these cells to reach a maximumcondition, thereby generating a relatively high signal. With a documentpresent in path 12 across aperture 24, the intensity of the radiatedlight is attenuated, thereby causing cells 32 and 33 to generate arelatively lower signal.

Cell 30 is positioned to detect an overlapped document condition andproduces a signal indicative thereof. Light diffused by its passagethrough a single document will impinge on cell 30 and cause it togenerate a relatively high signal while light diffused by overlappeddocuments reduces approximately 50 percent the value of this generatedsignal. With no document present in path 12 over aperture 24, cell 30generates little signal.

The signal produced by cell 30 is proportional to the amount of lightimpinging on its light sensitive surface as hereinbefore described,hence a thin document will affect the generation of a relatively largersignal than a thick document. To prevent these variations from resultingin erroneous signals, the output leads 35 of cell 30 are coupled to anautomatic gain control AGC amplifier 36 of control circuit 39 whichautomatically regulates the high signal produced by the cell to apredetermined level. Identical automatic gain control amplifiers 36 arealso coupled to the output leads 35 of cells 32 and 33 to automaticallyregulate the signals produced by these cells which may vary with lightsource intensity variations and the like. An AGC amplifier suitable foruse in this environment is disclosed in my copending US. Pat.application filed on Aug. 9, I968, Ser. No. 751,581, entitled AutomaticGain Control Circuit for Photocell Amplifiers," assigned to the assigneeof this invention. However, it is not intended that the use of thisinvention be restricted for use in conjunction with a particularamplifier.

The gain of amplifier 36 slowly increases after the passage of the lastdocument in a batch, and quickly and automatically adjusts to a levelcommensurate with the first document of a new batch, thereby providingautomatic regulation of signal values which may vary between batches ofdocuments. The simplified logic diagram illustrated in FIG. 3 disclosesthe output signals of cells 30, 32 and 33 coupled to amplifier 36, whichregulates and couples representative output signals through thresholdcircuits 40 to AND gate 37. The threshold circuits 40 may be thewell-known Schmitt trigger circuit which produces an output voltageof agiven level in response to input voltages which exceed a predeterminedthreshold level. The circuits 40 are employed to prevent erroneoussignals from being generated by minor voltage changes that may be causedby dark spots on a document, slight variations of document thicknesswithin a batch, perforated documents and the like.

AND gate 37 performs the logical function of conjunction and willproduce an overlapped document output signal when, and only when, allthe signals applied thereto are at a given level. By proper design, asexplained in the copending application, the AGC amplifiers 36 canprovide output signals varying from a reference or zero potential withmaximum light intensity on the cells to an output signal of L-V withminimum light intensity on the cells.

The sequence and timing of the signals applied to AND gate 37 are shownby waveforms A, B, and C in FIG. 4. The output of cells 32 and 33(waveforms A and B) are biased to a low voltage reference level when thesignal produced by the cells is at a regulated maximum, and will beconsidered at a higher voltage level when the signal produced by thecells decreases. As seen in FIG. 4, the output signals of cells 32 and33 (waveforms A and B) will go from a low voltage level (no documentpresent) to a high voltage level (document present), thus transmittingtwo of the necessary signals for conjunction in AND gate 37 to itsterminals A and B. The output signal of cell 30, (represented bywaveform C), is biased to a high voltage level +V when no document ispresent, and will go to a low voltage level 0V when it receives thelight diffused by a single document, and rises to an intermediatevoltage level +V when it receives light diffused by its passage throughoverlapped documents. AND gate 37 will produce an output signal onlywhen the input signal from cell 30 is at an intermediate level and cells32 and 33 are at their highest voltage level. The portion of waveform Cthat is shown in dashed lines indicates the signal produced by cell 30upon the occurrence of overlapped documents. The leading edge of thislatter portion of the signal indicates the time at which the overlappingof the documents occurs.

The level changes of wavefonns A and B occur at different times, as seenin FIG. 4, due to the physical positioning of cells 32 and 33 ashereinbefore described. This time differential pennits the detectorsystem to generate an overlapped document signal between the timesindicated by t and thus rendering the system incapable of producing anoverlapped document signal during the entry and exit of a document fromthe path between the sensor and the light source. if the detector systemwas operative during the gaps between successively transporteddocuments, cell 30 would change from low voltage level signal (singledocument) to a high voltage level signal (no document) and during thetransition would produce an intermediate signal indicative of overlappeddocuments.

While the principles of the invention have now been made clear in apreferred embodiment, there will be immediately obvious to those skilledin the art many modifications of structure, arrangement, proportions,the elements, materials, and components used in the practice of theinvention, and otherwise which are particularly adapted for specificenvironments and operating requirements without departing from theseprinciples. The appended claims therefore intend to cover and embraceany such modifications within the limits only of the true spirit andscope of the invention.

lclaim:

1. An apparatus for detecting overlapped documents transported along adocument path comprising: a light source positioned adjacent to one sideof the document path; a light sensi' tive element disposed on the otherside of the document path substantially opposite to said light source;and means for shielding said light sensitive element from directlyradiated light from said light source, so that said light sensitiveelement will detect only diffused light, said light sensitive elementproducing a first signal in response to diffused light transmittedthrough a single document and producing a second signal in response todiffused light transmitted through overlapped documents.

2. The apparatus as described in claim 1 wherein said means forshielding said light sensitive element from directly radiated light fromsaid light source comprises a housing within which said light sensitiveelement is mounted, at least a part of said housing providing theshielding for said light sensitive element.

3. A system for detecting overlapped documents transported along adocument path comprising: a light source positioned adjacent to one sideof said document path; and a sensor disposed on the other side of saiddocument path and substantially opposite to said light source, saidsensor comprising a housing, said housing defining a cavity, and a lightsensitive device disposed within said cavity, said light sensitivedevice being shielded within said cavity from directly radiated lightand adapted to produce a first signal indicative of diffused lighttransmitted through-a single document moving along said path past saidlight source and a second signal indicative of diffused lighttransmitted through overlapped documents moving along said path pastsaid light source.

4. A system for detecting overlapped documents transported along adocument path and controlling further movement of the documents when anoverlapped condition occurs comprising: alight source positionedadjacent one side of the document path; a document sensor positionedadjacent the other side of the document path substantially in alignmentwith said light source, said sensor comprising a first detector meansfor detecting a document in the path between said sensor and said lightsource and for generating a first signal representative of the presenceof the document, a second detector means for detecting overlappeddocuments in the path between said sensor and said light source,shielding means for shielding said second detector means from directlyradiated light from said light source, said second detector means beingresponsive to diffused light transmitted through overlapped documentsand producing a second signal in response thereto; and control means forcontrolling further movement of the documents along the document path inresponse to said first and second signals.

5. A system for detecting overlapped documents transported along adocument path comprising: a light source positioned adjacent to one sideof said document path; a document sensor positioned adjacent to theother side of said document path and substantially in alignment withsaid light source, said sensor comprising a housing, said housingdefining a cavity, a first light sensitive element mounted within saidcavity, said first light sensitive element being shielded from directlyradiated light within said cavity, said first light sensitive elementproducing a first signal indicative of diffused light transmittedthrough a single document moving along said document path past saidlight source and a second signal indicative of diffused lighttransmitted through overlapped documents moving along said document pathpast said light source, second and third light sensitive elementsmounted within said housing on opposite sides of said first lightsensitive element, said second and third light sensitive elements eachproducing a signal representative of a document present in said pathbetween said sensor and said light source; and means for transmitting anoverlapped document signal upon the occurrence of the signals producedby said second and third light sensitive elements and the second signalproduced by said first light sensitive element.

6, An overlapped document detector system as described in claim 5wherein said means for transmitting an overlapped document signalcomprises an AND gate, the input signals of which are the signalsproduced by each of said first, second and third light sensitiveelements.

7. A system for detecting overlapped documents transported along adocument path comprising: a light source positioned adjacent one side ofsaid document path; a housing positioned adjacent the other side of saiddocument path and in alignment with said light source; a sensorcomprising a first light sensitive element mounted within said housingso as to be shielded from directly radiated light from said lightsource, said first light sensitive element adapted to produce a firstsignal indicative of diffused light transmitted through a singledocument and a second signal indicative of diffused light transmittedthrough overlapped documents; second and third light sensitive elementsmounted within said housing adjacent said path on opposite sides of saidfirst light sensitive element, said second and third light sensitiveelements each producing a signal in response to the presence of adocument in said path between said light source and said sensor; meansfor automati cally adjusting the signals produced by said first, secondand third light sensitive elements to compensate for signal variancesbetween successively transported batches of documents; and an AND gatecoupled to receive the output signals of said light sensitive elements,said AND gate transmitting an output signal upon the occurrence of thesignals generated by said second and said third light sensitive elementsand said second signal generated by said first light sensitive element.

8. An apparatus for detecting overlapped documents transported along adocument path comprising: a light source positioned adjacent one side ofthe document path; a light sensitive element disposed on the other sideof the document path and substantially opposite to said light source;means for shielding said light sensitive element from directly radiatedlight from said light source, so that said light sensitive element willreceive only diffused light, said light sensitive element producing afirst signal in response to diffused light transmitted through a singledocument and producing a second signal in response to diffused lighttransmitted through overlapped documents; and means for controlling thesensitivity of said light sensitive element to compensate for signalvariances between successively transported batches of documents.

9. A system for detecting overlapped documents transported along adocument path comprising: a light source positioned adjacent one side ofsaid document path; a sensor disposed on the other side of said documentpath and substantially opposite to said light source, said sensorcomprising a housing, said housing defining a cavity, and a lightsensitive device disposed within said cavity, said light sensitivedevice being shielded within said cavity from directly radiated lightand adapted to produce a first signal indicative of diffused lighttransmitted through a single document moving along said path past saidlight source and a second signal indicative of diffused lighttransmitted through overlapped documents moving along said path pastsaid light source; and means for automatically adjusting the level ofsaid first and second signals to compensate for signal variances betweensuccessively transported batches of documents.

10. A system for detecting overlapped documents transported along adocument path comprising: a light source positioned adjacent one side ofsaid document path; a document sensor positioned adjacent the other sideof said document path and substantially in alignment with said lightsource, said sensor comprising a housing, said housing defining acavity, a light sensitive element mounted within said cavity, said lightsensitive element being shielded from directly radiated light

1. An apparatus for detecting overlapped documents transported along adocument path comprising: a light source positioned adjacent to one sideof the document path; a light sensitive element disposed on the otherside of the document path substantially opposite to said light source;and means for shielding said light sensitive element from directlyradiated light from said light source, so that said light sensitiveelement will detect only diffused light, said light sensitive elementproducing a first signal in response to diffused light transmittedthrough a single document and producing a second signal in response todiffused light transmitted through overlapped documents.
 2. Theapparatus as described in claim 1 wherein said means for shielding saidlight sensitive element from directly radiated light from said lightsource comprises a housing within which said light sensitive element ismounted, at least a part of said housing providing the shielding forsaid light sensitive element.
 3. A system for detecting overlappeddocuments transported along a document path comprising: a light sourcepositioned adjacent to one side of said document path; and a sensordisposed on the other side of said document path and substantiallyopposite to said light source, said sensor comprising a housing, saidhousing defining a cavity, and a light sensitive device disposed withinsaid cavity, said light sensitive device being shielded within saidcavity from directly radiated light and adapted to produce a firstsignal indicative of diffused light transmitted through a singledocument moving along said path past said light source and a secondsignal indicative of diffused light transmitted through overlappeddocuments moving along said path past said light source.
 4. A system fordetecting overlapped documents transported along a document path andcontrolling further movement of the documents when an overlappedcondition occurs comprising: a light source positioned adjacent one sideof the document path; a document sensor positioned adjacent the otherside of the document path substantially in alignment with said lightsource, said sensor comprising a first detector means for detecting adocument in the path between said sensor and said light source and forgenerating a first signal representative of the presence of thedocument, a second detector means for detecting overlapped documents inthe path between said sensor and said light source, shielding means forshielding said second detector means from directly radiated light fromsaid light source, said second detector means being responsive todiffused light transmitted through overlapped documents and producing asecond signal in response thereto; and control means for controllingfurther movement of the documents along the document path in response tosaid first and second signals.
 5. A system for detecting overlappeddocuments transported along a document path comprising: a light sourcepositioned adjacent to one side of said document path; a document sensorpositioned adjacent to the other side of said document path andsubstantially in alignment with said light source, said sensorcomprising a housing, said housing defining a cavity, a first lightsensitive element mounted within said cavity, said first light sensitiveelement being shielded from directly radiated light within said cavity,said first light sensitive element producing a first signal indicativeof diffused light transmitted through a single document moving alongsaid document path past said light source and a second signal indicativeof diffused light transmitted through overlapped documents moving alongsaid document path past said light source, second and third lightsensitive elements mounted within said housing on opposite sides of saidfirst light sensitive element, said second and third light sensitiveelements each producing a signal representative of a document present insaid path between said sensor and said light source; and means fortransmitting an overlapped document signal upon the occurrence of thesignals produced by said second and third light sensitive elements andthe second signal produced by said first light sensitive element.
 6. Anoverlapped document detector system as described in claim 5 wherein saidmeans for transmitting an overlapped document signal comprises an ANDgate, the input signals of which are the signals produced by each ofsaid first, second and third light sensitive elements.
 7. A system fordetecting overlapped documents transported along a document pathcomprising: a light source positioned adjacent one side of said documentpath; a housing positioned adjacent the other side of said document pathand in alignment with said light source; a sensor comprising a firstlight sensitive element mounted within said housing so as to be shieldedfrom directly radiated light from said light source, said first lightsensitive element adapted to produce a first signal indicative ofdiffused light transmitted through a single document and a second signalindicative of diffused light transmitted through overlapped documents;second and third light sensitive elements mounted within said housingadjacent said path on opposite sides of said first light sensitiveelement, said second and third light sensitive elements each producing asignal in response to the presence of a document in said path betweensaid light source and said sensor; means for automatically adjusting thesignals produced by said first, second and third light sensitiveelements to compensate for signal variances betweEn successivelytransported batches of documents; and an AND gate coupled to receive theoutput signals of said light sensitive elements, said AND gatetransmitting an output signal upon the occurrence of the signalsgenerated by said second and said third light sensitive elements andsaid second signal generated by said first light sensitive element. 8.An apparatus for detecting overlapped documents transported along adocument path comprising: a light source positioned adjacent one side ofthe document path; a light sensitive element disposed on the other sideof the document path and substantially opposite to said light source;means for shielding said light sensitive element from directly radiatedlight from said light source, so that said light sensitive element willreceive only diffused light, said light sensitive element producing afirst signal in response to diffused light transmitted through a singledocument and producing a second signal in response to diffused lighttransmitted through overlapped documents; and means for controlling thesensitivity of said light sensitive element to compensate for signalvariances between successively transported batches of documents.
 9. Asystem for detecting overlapped documents transported along a documentpath comprising: a light source positioned adjacent one side of saiddocument path; a sensor disposed on the other side of said document pathand substantially opposite to said light source, said sensor comprisinga housing, said housing defining a cavity, and a light sensitive devicedisposed within said cavity, said light sensitive device being shieldedwithin said cavity from directly radiated light and adapted to produce afirst signal indicative of diffused light transmitted through a singledocument moving along said path past said light source and a secondsignal indicative of diffused light transmitted through overlappeddocuments moving along said path past said light source; and means forautomatically adjusting the level of said first and second signals tocompensate for signal variances between successively transported batchesof documents.
 10. A system for detecting overlapped documentstransported along a document path comprising: a light source positionedadjacent one side of said document path; a document sensor positionedadjacent the other side of said document path and substantially inalignment with said light source, said sensor comprising a housing, saidhousing defining a cavity, a light sensitive element mounted within saidcavity, said light sensitive element being shielded from directlyradiated light within said cavity, said light sensitive elementproducing a first signal indicative of diffused light transmittedthrough a single document moving along said document path past saidlight source and a second signal indicative of diffused lighttransmitted through overlapped documents moving along said document pathpast said light source; means for detecting the presence of a documentin said path between said light source and said document sensor and forproducing a third signal indicative thereof; and means for transmittingan overlapped document signal upon the occurrence of said second andthird signals.